The present invention relates to a refrigerating unit which has a plurality of compressors installed in parallel and controls the operation capacity according to the load to be refrigerated, and this refrigerating unit is most suitable to a configuration that includes an inverter-driven compressor and constant-speed compressors.
In refrigerating units incorporating an inverter-driven compressor and constant-speed compressors, it has been known to additionally put the constant-speed compressor into operation and reduce the driving frequency of the inverter-driven compressor when the driving frequency of the inverter-driven compressor has reached the maximum value and the load further increases. In conjunction with this, a method worthy to note here has been disclosed in JP-A-09-273819, in which when switching over the operation from the inverter-driven compressor to the constant-speed compressor, the inverter-driven compressor is brought to a halt for a fixed period of time to decrease the operation time of the inverter-driven compressor to thereby improve the reliability of the inverter-driven compressor.
Since in the prior art mentioned above the driving frequency of the inverter-driven compressor is lowered or the inverter-driven compressor is stopped from operating for a fixed period in response to changes in load, it has been difficult to finely control the operation capacity in response to varying load, and there has been a possibility that the load capacity and the operation capacity become unmatched.
The object of the present invention is to make it possible to finely vary the operation capacity in response to changes in load, enable optimum operation according to load, and thereby achieve a reduction in energy consumption.
According to an aspect of the present invention made to achieve the above object, in a refrigerating unit having an inverter-driven compressor using a variable driving frequency, and constant-speed compressors using a constant driving frequency, the refrigerating unit comprising a pressure sensor installed on the suction side of the inverter-driven compressor and constant-speed compressors, means for starting the inverter-driven compressor first, and means for deciding a driving frequency for the inverter-driven compressor or deciding the number of compressors to operate, based on a suction pressure value detected by the pressure sensor after the inverter-driven compressor is started.
Because the operation of the inverter-driven compressor is started first, it is possible to obtain a smooth starting of the operation of the refrigerating unit in accordance with load when the unit is started. After this, the driving frequency of the inverter-driven compressor or the number of compressors to operate is decided based on the suction pressure value of the compressors. Therefore, even if there is a great change in refrigerating load, a sufficient capacity can be secured in accordance with this great change of load, and the capacity can be finely controlled. Thus, it is possible to perform the operation with optimum operation capacity with respect to load and thereby reduce energy consumption.
In the above operation, when the suction pressure value rises above a specified value, it is desirable to start one or more constant-speed compressors regardless of the driving frequency of the inverter-driven compressor.
Further in the above operation, when the suction pressure value falls below a specified value, it is desirable to stop the constant-speed compressors regardless of the driving frequency of the inverter-driven compressor.
Further in the above operation, it is desirable to start the constant-speed compressors one by one after the driving frequency of the inverter-driven compressor has reached the maximum value.
Further in the above operation, it is desirable to stop the constant-speed compressors one by one after the driving frequency of the inverter-driven compressor has reached the minimum value.
Further in the above operation, it is desirable to decide the maximum and minimum values of the driving frequency of the inverter-driven compressor, start the constant-speed compressors one by one after the maximum frequency has been reached, and stop the constant-speed compressors one by one after the minimum frequency has been reached.
According to another aspect of the present invention, in a refrigerating unit having an inverter-driven compressor using a variable driving frequency, and constant-speed compressors using a constant driving frequency, the refrigerating unit comprising an inverter-driven compressor of scroll type and constant-speed compressors of scroll type, and a pressure sensor installed on the suction side of the inverter-driven compressor and constant-speed compressors, and when a value detected by the pressure sensor at the start of the operation is greater than a preset value, an inverter-driven compressor and a constant-speed compressor are started, and thereafter the driving frequency of the inverter-driven compressor and the number of constant-speed compressors to operate are decided.
Because the inverter-driven compressor and a constant-speed compressors are started when the suction pressure value of the compressors is greater than a preset value at the start of the operation, a sufficient operation capacity relative to load can be secured at the start of the operation, and even if there is a sudden increase in load, a smooth starting can be obtained in response to this sudden load increase.
Thereafter, the driving frequency of the inverter-driven compressor and the number of constant-speed compressors to operate are decided based on a suction pressure value of the compressors. In consequence, a sufficient capacity can be secured according to load and fine control of capacity can be realized.
According to a further aspect of the present invention, in a refrigerating unit having an inverter-driven compressor using a variable driving frequency, and constant-speed compressors using a constant driving frequency, the refrigerating unit comprising an inverter-driven compressor of scroll type and constant-speed compressors of scroll type, and a pressure sensor installed on the suction side of the inverter-driven compressor and constant-speed compressors, and the driving frequency of the inverter-driven compressor and the number of constant-speed compressors to operate are decided based on a suction pressure value detected by the pressure sensor, and the capacity can be controlled in a wide range of 15% to 100%.
Because the driving frequency of the inverter-driven compressor and the number of constant-speed compressors to operate are decided based on a suction pressure value and the capacity control range is from 15% to 100%, an optimum operation capacity with respect to conceivable load of an air conditioner can be obtained, which makes it possible to achieve a reduction in energy consumption.
According to an additional aspect of the present invention, in a refrigerating unit having an inverter-driven compressor using a variable driving frequency, and constant-speed compressors using a constant driving frequency, the refrigerating unit comprising an inverter-driven compressor of scroll type and constant-speed compressors of scroll type, a pressure sensor installed on the suction side of the inverter-driven compressor and constant-speed compressors, means for deciding a driving frequency of the inverter-driven compressor and the number of the constant-speed compressors to operate, based on a suction pressure value detected by the pressure sensor, and means for determining a failure of the inverter for driving the inverter-driven compressor, and when the inverter is determined to be out of order by the failure-determining means, capacity control is continued by changing the number of compressors to operate, including the inverter-driven compressor and the constant-speed compressors.
Even when the inverter is faulty, the capacity control is continued by changing the number of compressors to operate, including the inverter-driven compressor and the constant-speed compressors. Thus stepwise capacity control can be continued even if frequency control is not performed.
According to yet another aspect of the present invention, in a refrigerating unit having an inverter-driven compressor using a variable driving frequency and constant-speed compressors using a constant driving frequency, the refrigerating unit comprising an inverter-driven compressor of scroll type and constant-speed compressors of scroll type, a pressure sensor installed on the suction side of the inverter-driven compressor and constant-speed compressors, means for starting the operation of the inverter-driven compressor first when a suction pressure value (Ps) detected by the pressure sensor is greater than a preset value (PsU), means for decreasing the driving frequency of the inverter-driven compressor according to a difference between the suction pressure value (Ps) and the preset value (PsU) when the suction pressure value has risen above a specified value (C) after the inverter-driven compressor is started, and means for starting a constant-speed compressor after the driving frequency is decreased.
Because the operation of an inverter-driven compressor is started first when the suction pressure value (Ps) is greater than a preset value and the driving frequency of the inverter-driven compressor is decreased according to a difference between the suction pressure value (Ps) and a preset value (PsU) when the suction pressure value has risen above a specified value (C) and a constant-speed compressor is started when the driving frequency has been decreased, a change in the operation capacity can be made small even if the number of compressors operated is changed and therefore a sufficient capacity can be secured with respect to changes in load and even finer capacity control can be implemented.